Embodiments of the invention relate to the field of propulsion units for aquatic vehicles, such as ships, submarines, or oil platforms.
These propulsion units, also known as “Propulsion-Oriented Drive” or “POD”, generally consist of a movable casing mounted in a pivot connection in relation to a hull element of the aquatic vehicle. The hull element may be e.g. the stern or the prow of a ship. The propulsion unit consists of a propulsion element, which may be e.g. a propeller, integral with a drive shaft rotatably mounted inside the mobile casing and capable of being rotated by means of an electrical machine.
Such a propulsion unit may include rotary bearings provided to permit rotation of the drive shaft in relation to the mobile casing. To limit friction, these bearings may consist of a closed space containing a hydraulic fluid, such as oil or water. Sealing devices, such as gaskets, delimit the closed spaces and have the function of preventing leakage of hydraulic fluid from these closed spaces.
The bearings are often subjected to high mechanical stresses, in particular when the rotation of the drive shaft and the propulsion element occurs over long periods of time. These stresses result in heating of the hydraulic fluid contained in the closed space and the loss of its lubricating properties. This results in premature wear on the bearings.